Chiral quinolinyl-oxazolines as ligands for copper(I)-catalyzed asymmetric cyclopropanation

Chiral quinolinyl-oxazoline compounds have been synthesized from enantiomerically pure amino alcohols and 8-quinoline-carboxylic acid using a convenient procedure. Asymmetric cyclopropanation of styrene with diazoacetates in the presence of 1 mol% of CuOTf and quinolinyl-oxazolines gave 2-phenylcyclopropane carboxylates in moderate enantiomeric excesses.     

Bis(oxazoline)copper complexes covalently bonded to insoluble support as catalysts in cyclopropanation reactions.

Chiral bis(oxazolines) are readily dialkylated in the methylene bridge, opening the way to immobilization at that position, keeping the C(2) symmetry of the chiral ligand. Bis(oxazolines) functionalized with two allyl or vinylbenzyl groups are easily grafted onto mercaptopropylsilica. Another approach to immobilization is the polymerization of the ligands bearing vinylbenzyl groups to yield insoluble polymers. The Cu(OTf)(2) complexes of the immobilized ligands promote the enantioselective cyclopropanation reaction between styrene and ethyl diazoacetate. The results depend on the nature of the support and the method of immobilization. With regard to the type of solid, the best results, which are similar to or even better than those obtained with the corresponding dibenzylated homogeneous catalysts, are obtained with homopolymers. With regard to the bis(oxazoline), that bearing indan groups leads to good results both onto silica and polymers, whereas with the ligand bearing tert-butyl groups good enantioselectivities are only obtained with homopolymeric catalysts. Some of the heterogeneous catalysts can be easily recovered and reused, as much as five times, with the same yield and stereoselectivities.     

Chiral metal-organic frameworks with tunable open channels as single-site asymmetric cyclopropanation catalysts

A pair of interpenetrated and non-interpenetrated chiral metal-organic frameworks with the same catalytic sites but different open channel sizes catalysed asymmetric cyclopropanation of substituted terminal alkenes with excellent diastereoselectivities (up to 9.6) and enantioselectivities (up to >99%).     

Vitamin B12 derivatives as natural asymmetric catalysts: enantioselective cyclopropanation of alkenes

Vitamin B(12) derivatives were found for the first time to be general and efficient catalysts for asymmetric cyclopropanation of alkenes with ethyl diazoacetate (EDA). Among several common derivatives, aquocobalamin (B(12a)) was shown to be the most effective catalyst for a variety of alkenes, providing cis-dominant cyclopropanes in excellent yields and moderate enantioselectivity. Reactivity studies under different conditions suggest that the active species in the proposed catalytic cycle is the base-on cob(II)alamin (B(12r)) that is generated possibly via in situ reduction of B(12a) by EDA.     

手性金属催化剂在不对称环丙烷化反应中的应用进展

手性金属催化剂在不对称环丙烷化反应中的应用一直是不对称合成领域的一个热点。对三十多年来的这一领域的手性金属催化剂的发展作了详细的归纳和评述。     

Chiral Phebox-rhodium complexes as catalysts for asymmetric direct aldol reaction

Chiral bis(oxazolinyl)phenyl-rhodium complexes act as catalysts in the combination of AgOTf for direct aldol reaction of ketones and aromatic aldehydes to give the corresponding β-hydroxyketones in high anti-selectivity and a good to high enantioselectivity up to 91% ee.     

Polymer-supported Bis(oxazoline)-copper complexes as catalysts in cyclopropanation reactions

Bis(oxazolines) are easily immobilized by functionalization of the central methylene bridge with polymerizable groups and subsequent polymerization. Polymers are transformed into copper catalysts active in the cyclopropanation of styrene with ethyl diazoacetate. The results are similar or even better than those obtained with the similar homogeneous systems, and the catalysts can be easily recovered and reused. The substitution in the methylene bridge leads to a slight reduction in the enantioselectivity and an unexpected cis-preference.     

简单烯烃不对称环氧化的手性金属配合物催化剂

介绍了多类简单烯烃不对称环氧化反应的手性过渡金属配合物催化剂系统的催化效果。论述了配体结构与配合物作为环氧化反应催化剂的活性，稳定性，催化效率的关系。从配合物的电子和立体因素，几何构型与过渡态的构象和非对映异构体的能量差别探讨对不对称诱导效果的影响。同时陈述机理的研究情况。     

Supramolecular double helical Cu(I) complexes for asymmetric cyclopropanation

Chiral double-stranded helicates, formed between Cu(I) ion and C(2)-symmetric oligopyridines, were used for catalytic asymmetric cyclopropanation of alkenes; low catalyst loadings (0.2 mol%), high TONs (up to 404) and short reaction times (30-60 min) were achieved with [Cu(2)L(2)]OTf(2)(L = chiral C(2)-symmetric terpyridine).     

Palladocarbosilane dendrimers as catalysts for the asymmetric hydrovinylation of styrene in supercritical carbon dioxide

The palladocarbosilane dendrimers 2 and 3, containing the P-stereogenic phosphine [P(2-biphenylyl)PhCH₂] fragment, and the model compound Me₃Si(P(2-biphenylyl)PhCH₂)(PdCl(η³-2-MeC₃H₄)), 1, were tested as precatalysts in the hydrovinylation of styrene, in supercritical CO₂ medium. Na[BARF] was used as a cocatalyst. In all cases, the activity was somewhat less than that observed in CH₂Cl₂, but the selectivity and enantiomeric excess were excellent and comparable with the results obtained using the conventional solvent.     

Ruthenium amino carboxylate complexes as asymmetric hydrogen transfer catalysts

The synthesis and characterization of optically active amino carboxylate complexes of formula [(η(6)-arene)Ru(Aa)Cl] (arene = C(6)H(6), C(6)Me(6), Aa = amino carboxylate) as well as those of the related trimers [{(η(6)-arene)Ru(Aa)}(3)][BF(4)](3) are reported. Trimerization takes place with chiral self-recognition: only diastereomers equally configured at the metal, R(Ru)R(Ru)R(Ru) or S(Ru)S(Ru)S(Ru), are detected. The crystal structures of the complexes [(η(6)-C(6)H(6))Ru(Pip)Cl] and [{(η(6)-C(6)Me(6))Ru(Pro)}(3)][BF(4)](3) have been determined by X-ray diffraction methods. Both types of complexes catalyse the hydrogen transfer reaction from 2-propanol to ketones with moderate enantioselectivity (up to 68% ee). The enantiodifferentiation achieved can be accounted for by assuming that Noyori's bifunctional mechanism is operating.     

New chiral Schiff base–Cu(II) complexes as cyclopropanation catalysts

A series of chiral Schiff base ligands 1–4, derived from (1R,2S)-(+)-cis-1-amino-2-indanol and other chiral amines with substituted salycilaldehydes were synthesized and transformed to the corresponding Cu(II) complexes. Molecular structures of six Cu(II) complexes were determined by X-ray crystallographic studies. The structures show the metal ion in a distorted square planar geometry with dimeric or monomeric structures, depending on the ligand denticity. The potential use of these complexes in asymmetric Cyclopropanation was explored.     

A non-fluorous copper catalyst for the styrene cyclopropanation reaction in a fluorous medium

The complex Tp(Br3)Cu(NCMe) (1), containing no fluorine atoms, can be dissolved in the perfluoropolyether FOMBLIN and employed as a catalyst for the styrene cyclopropanation reaction with ethyl diazoacetate, with activities and diastereo-selectivities identical to those observed under homogeneous conditions with the advantage of being able to use a fluorous separation technique for catalyst recycling.     

A positive nonlinear effect in catalytic asymmetric cyclopropanation of styrene with ethyl diazoacetate

The existence of a positive nonlinear effect [(+)-NLE] in the asymmetric cyclopropanation of styrene with ethyl diazoacetate catalysed by a chiral Cu(I)-bisoxazoline complex was observed. This effect can be explained by the possible formation of a catalytically inactive heterochiral meso-complex.     

Arylid-OX and Arylid-BOX derived catalysts: applications in catalytic asymmetric cyclopropanation

A novel family of chiral non-racemic monodentate oxazoline ligands known as Arylid-OXs 1a and 1b was prepared in good overall yields. These ligands were screened in bench-mark Cu(I)-catalyzed cyclopropanations and gave ees as high as 58%. Both ¹H NMR and computational studies using 1a indicated that the active catalyst was most likely to be the di-coordinated complex, Cu(I)-1a₂(MeCN)₂. Two novel ortho-substituted Arylid-BOX ligands 2a and 2b were also synthesized in very good yields. These ligands were tested in the same reaction as for 1a and 1b and, although excellent yields could be obtained with 2b, which is assumed to be due to an electron-donating effect from the ortho-methoxy group, a best ee of only 56% was obtained with 2a. In fact, both the enantioselectivities and diastereoselectivities obtained with these ortho-substituted ligands were in line with those previously obtained with the para-substituted series.     

Orthopalladated complexes as phase-transfer catalysts for asymmetric alkylation of achiral Schiff base esters

The asymmetric C-alkylation of benzophenone Schiff base glycine esters has been achieved using a palladium(II) chiral complex as a phase-transfer catalyst. The aromatic moiety around the metal center and various physicochemical parameters were investigated to study their effect on the asymmetric alkylation reaction under phase-transfer conditions. Moderate enantioselectivity(30–40%) was achieved under room temperature conditions, which is a significant improvement compared to no enantioselectivity with a chiral palladium-salen complex reported earlier. Computer simulation studies indicate that coordination of the metal center with Z-enolate forming a square planar complex provides a favorable steric environment where the α-carbon atom of the enolate is available for enantioselective alkylation.     

Highly efficient chiral copper Schiff-base catalyst for asymmetric cyclopropanation of 2,5-dimethyl-2,4-hexadiene

A remarkable increase in catalytic activity is found for the asymmetric cyclopropanation of 2,5-dimethyl-2,4-hexadiene with diazoacetate by use of the chiral copper Schiff-base complexes, which are derived from substituted salicylaldehydes, chiral aminoalcohols, and copper acetate monohydrate. Furthermore, a combination of a chiral copper Schiff-base with a Lewis acid showed an increase in yield (up to 90%) and in enantioselectivity (up to 90% ee) for the asymmetric cyclopropanation of the diene with t-butyl diazoacetate at 20 °C.     

Binuclear copper complexes with non-steroidal anti-inflammatory drugs as studied by electrospray ionization mass spectrometry

The solutions containing one of the copper salts (CuCl₂, Cu(ClO₄)₂, Cu(NO₃)₂, and CuSO₄) and one of the non-steroidal anti-inflammatory drugs (NSAIDs, ibuprofen, ketoprofen or naproxen) were analyzed by electrospray ionization mass spectrometry. Three of the salts, namely CuCl₂, Cu(ClO₄)₂ and Cu(NO₃)₂, yielded binuclear complexes of drug:metal stoichiometry 1:2. Existence of the complexes of such stoichiometry has not been earlier observed. For copper(II) chloride the complexes (ions of the type [M-HCOOH+Cu₂Cl]⁺ and [M+Cu₂Cl]⁺, M stands for the drug molecule) were formed in the gas phase. When copper(II) perchlorate or copper(II) nitrate was used, the observed binuclear copper complexes (ions of the type [M-H+Cu₂(ClO₄)₂+CH₃OH]⁺, [M-H+Cu₂(ClO₄)₂]⁺ and [M-H+Cu₂(NO₃)₂+CH₃OH]⁺, [M-H+Cu₂(NO₃)₂]⁺) were observed at low cone voltage, thus these complexes must have already existed in the solution analysed. Therefore, such complexes may also exist under physiological conditions.